[DllImport] in asp.net

Hello ...!
I want to import a dll in asp.net, and I have a major problem
First i want to say that this dll works fine in a windows application written in C#, the dll importation works just fine. and this dll works file when I run this code in FileSystem Mode (in ASP.net )
But when I run the this code in Localhost ,I don't get anything back, nothing, not even an error.
Can it be something with the security rights the IIS has? or Web.config? or my Import?

Example Code :

[DllImport("Mydll.dll")]
public static extern int LogIn(int handle);


Please Help me ... Please .... ...